The present invention relates to fiber-optic communications network equipment, and more particularly, to depolarizers for optical channel monitors in optical network equipment such as optical amplifiers.
Fiber-optic networks are used to support-voice and data communications. In optical networks that use wavelength division multiplexing, multiple wavelengths of light are used to support multiple communications channels on a single fiber.
Optical amplifiers are used in fiber-optic networks to amplify optical signals. For example, optical amplifiers may be used to amplify optical data signals that have been subject to attenuation over fiber-optic paths. A typical amplifier may include erbium-doped fiber coils that are pumped with diode lasers. Raman amplifiers have also been investigated. Discrete Raman amplifiers may use coils of dispersion-compensating fiber to provide Raman gain. Distributed Raman amplifiers.provide gain in the transmission fiber spans that are used to carry optical data signals between network nodes.
It is an object of the present invention to provide optical network equipment such as optical amplifiers that have optical channel monitors.
It is also an object of the present invention to provide depolarizers for optical channel-monitors and other devices in optical network equipment.
These and other objects of the invention are accomplished in accordance with the present invention by providing optical amplifiers and other optical network equipment for use in fiber-optic communications links in fiber-optic networks. The fiber-optic links may be used to carry optical data signals associated with wavelength-division-multiplexing channels.
The equipment may include an optical tap for tapping optical signals in the equipment. The equipment may also include an optical channel monitor to which the tapped optical signals are provided. The optical channel monitor may measure the channel powers of the tapped optical signals. The measured channel power information may be used in controlling the equipment. For example, the measured channel powers or spectra may be used in controlling a dynamic filter in an optical amplifier to produce a desired gain spectrum or output power spectrum.
A depolarizer may be used to depolarize the tapped optical signals before the tapped optical signals are provided to the optical channel monitor. The depolarizer may be based on one or more lengths of birefringent fiber or a dynamic depolarizer. The use of the depolarizer may reduce errors in the measured channel powers by suppressing the effects of polarization dependent loss.
Further features of the invention and its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments.